The present invention concerns focussing systems of the type in which camera-to-subject distance is measured by the emission of ultrasonic acoustic radiation towards the subject with generation of a received-back signal when the radiation reflected back from the subject is received back at the camera, with the time of generation of the received-back signal being utilized to terminate operation of a timer which initiates upon radiation emission, the signal furnished by the timer upon termination of the timing operation accordingly being dependent upon the acoustically measured subject-distance.
Such systems are known. It is furthermore known to use the measured-subject-distance signal to control an indicator which informs the user of the direction in which he should manually move the camera's focus adjuster to correct the state of focus of the camera.